The invention relates to a method of monitoring for corrosion in sealed and more particularly liquid-filled spaces such as heat storage means and more specifically heating and cooling circuits of motor vehicles and to a system for performing the method.
Without any limitative intent, the invention is to be described with reference to such heating and cooling circuits, which constitute a preferred field of application of the invention, since they are equally suitable also for use in other sealed or sealable spaces where there is a corrosion hazard, such as for instance heat pipes or boilers. The invention may find application in all spaces in which there is a danger of corrosion and more particularly which are substantially filled with a liquid or contain a material which changes between different phases, more particularly between the liquid and the gaseous phase, or a gaseous material having moisture therein.
Modern heating and cooling circuits are hermetically sealed so that in normal operational circumstances the heat transfer medium, which circulates in the circuit and normally contains water, is not able to escape as vapor when its temperature exceeds its boiling point. For extreme situations a pressure relief valve is provided.
The heat transfer medium conveys the heat within the engine, from the engine to the vehicle heating system and from the engine to the cooling system. Heat storage means, more particularly in the form of latent heat storage means are incorporated in such heating and cooling circuits in order to store engine heat for operational conditions in which there is a thermal deficit, for instance for starting from cold.
The storage material utilized for storing with a high energy density is frequently such as to attack metals, which are employed in heating and cooling circuits, for example aluminum and copper. In the case of leakage of the heat storage material into the heat transfer medium it is possible for the escaping storage material to circulate and to cause corrosion, decomposition and the like so that respective damage will be caused.
Since such corrosion is normally accompanied by the formation of gaseous hydrogen, the pressure within the sealed heating and cooling liquid circuits will increase so that the hoses normally utilized in a part of the circuit will stretch, this leading to difficulties in the regulation of the level and may finally cause the pressure relief valve to open with the consequent loss of the heat transfer medium so that as a further consequence the engine has to be put out of operation.
Since the leakage of the heat storage material results in chemical and physical changes in the heat transfer medium, attempts have been made to detect such changes and to use them as leakage indicators. In this respect ionization and changes in the electrical conductivity are more particularly to be mentioned. Such measurements are however only possible with a comparatively large amount of apparatus complexity and are not necessarily conclusive, because the respective readings are inherently subject to large variations and because the sensors may readily be fouled. Furthermore the concentrations of leaked material are subject to considerable local variations so that the location of such sensors is made even more elaborate.